Microelectronic industries, as well as other related industries are constantly reducing the feature size for constructing microscopic structures. Effective lithographic techniques are essential in this quest and require constantly improved radiation sensitive materials (resists). In order to resolve smaller structures, the wavelength of the exposing light has been reduced into the deep UV regions of 248 nm, 193 nm and 157 nm in addition to exposure to EUV or x-ray radiation. As the patterns and wavelengths become finer, the material properties of the resists used for pattern delineation have become more and more demanding. In particular, requirements of sensitivity, transparency, aesthetics of the image produced, and the selectivity of the resists to etch conditions for pattern transfer become more and more strenuous.
Chemically amplified resists are used extensively for optical lithography and electron-beam writing (see “Solid State Technology,” Vol. 34 (1991), no. 8, pages 53 to 60) in the semiconductor industry. Chemically amplified resists operate on the principle of acid-catalyzed cleavage, wherein polar alkali solubilizing but blocked chemical groups, (e.g. carboxyl groups or phenolic hydroxyl groups) are unblocked by means of a photolytically generated acid. The resist changes polarity in the exposed regions and in many cases becomes alkali soluble. This change in polarity can be used, for example, to develop the resist in various ways, including an alkaline developer or—in the case of dry-developable resists—for selective silylation followed by oxidative plasma etching.
To satisfactorily obtain such acid catalyzed deblocking, the acid must diffuse in the solid state polymer matrix. The acid diffusion obtained is a function of numerous complicated and interacting variables. Examples of such various include acid strength, acid size, acid volatility, resin functional groups, time between exposure and post exposure bake, time and temperature of post exposure back, polymer functional groups and the presence or absence of basic or acidic contamination.
To obtain high resolution, in particular for pattern dimensions<0.25 um, control of the diffusion of the photoacid generated by exposure, is critical. Too much lateral diffusion produces narrow lines and too little lateral diffusion produces lines that are too wide. In addition it is necessary to control the diffusion vertically to generate vertical profiles despite exposures and absorptions that tend to generate a vertical exposure gradient. Similarly, basic contamination from the substrate or the atmosphere can generate photoacid neutralizing gradients in the resist, which need to be overcome.
The present invention provides new photoresist compositions comprising a non photo sensitive acid generating additive which provides a combination of high resolution, high photospeed, good exposure latitude, good depth of focus and good profiles.
Furthermore, photosensitive compositions wherein the resin binder contains an anhydride or a lactone group show significantly improved shelf life.